The attitude determination, i.e. the position and/or orientation determination, of an object, for example of a mobile machine, by means of a total station has long been known. For example, a reflective prism is mounted on the latter in a position known relative to the object and is measured by means of a total station having a laser beam. The reflected beam is received by the total station. By means of a phase or time difference of the emitted and the received beam, the distance from the reflector to the total station is derived and the solid angle of the object relative to the total station is determined on the basis of the emission direction of the beam, so that the position of the object can be determined.
Further measurements which are linked to the position and generally also require a knowledge of the orientation of the object in space are then carried out starting from a position determined by such a system. In principle, the orientation can also be derived from the position determination of two or more points. For applications involving measurement, the 6 degrees of freedom of the object, but at least the position and hence 3 degrees of freedom, have to be determined for unambiguously establishing the absolute position in space. The problem therefore comprises the determination of position and orientation as two tasks which can be achieved in principle separately but for many applications have to be carried out in association. As a rule, both position and orientation or alignment of an object are therefore required.
For the additional determination of the alignment of the object, systems of the prior art use, for example, a plurality of reflective elements which are mounted with known position relative to one another and to the machine. By measurement of the plurality of reflectors and by means of the known relative position of the reflectors to one another, the alignment of the machine is determined. A disadvantage of such systems is the complicated measurement of the plurality of reflective elements or the erection and operation of a plurality of total stations.
A further known possibility for determining the alignment of an object in a horizontal plane is the use of a compass.
The prior art also discloses the determination of the position of a mobile machine by means of a GPS receiver which, for example, is mounted on the machine or integrated in the machine. For additional determination of the alignment of the machine, however, at least two GPS receivers mounted a horizontal distance apart on the machine are required. The position of each individual receiver is determined on the basis of known GPS position determination and the alignment of the machine is determined by means of the known relative position of the receivers. However, visual contact with at least three, preferably at least four satellites must always exist for position determination via GPS, which however is not the case for work under bridges, in narrow passages between houses or due to other obscurations. Furthermore, the accuracy of measurement of the position, in particular of the vertical position, of a machine is lower in the case of satellite position determinations in comparison with the accuracy in geodetic surveys.
Consequently, with corresponding requirements, the use of high-precision optical measuring methods, as are known from geodesy, are still advantageous.
In a further known possibility for providing information about the orientation of a machine, the position of the machine is tracked and a direction of travel is determined from the changes in position. With the assumption that the direction of travel corresponds to a certain orientation of the machine, information about the orientation of the machine can be derived therefrom. A drift during the movement of the machine is not taken into account in this method.
WO 2006/070009 describes a method for determining the position and the alignment of an object using a rotating laser and two detectors. The rotating laser emits a horizontal laser beam which is associated with angle-dependent information and is received in each case by the two detectors mounted in a known position on the machine. The position and the alignment of the machine relative to the rotational laser are derived from the angle information received in each case and the positions of the detectors relative to one another.
The generally known methods and systems of the prior art for determining the position and the alignment of an object always require separate measuring processes to at least two measuring points a horizontal distance apart. This is frequently very complicated and may be inaccurate and unsuitable for certain requirements, such as, inter alia, for surveying an object having a very small horizontal dimension. As already mentioned, the limited nature of the potential uses of GPS systems are always disadvantageous.
WO 2006/097408 describes an attitude determination method for determining position and orientation of a unit. There, the approach is based on the determination of the position of the unit by a scanning system, for example a laser scanner. The determination of the orientation of the unit is effected by a measurement of the attitude of a receiver arranged on the unit relative to the beam axis of the radiation emitted by the scanning unit. From the knowledge of the attitude of the receiver relative to the beam axis and the knowledge of the attitude of the receiver relative to a carrier component of the unit, the orientation of the unit can be derived. Knowledge of the attitude in space thus follows from the position information and the orientation information.
Since the orientation is determined on the basis of an offset of the receiver relative to the beam axis, and the optical system of the receiver has only a limited opening angle, the alignment of the receiver must always correspond approximately to the beam axis or the beam axis must constantly attract the movement of the unit. At a fixed point in time, the receiver is therefore able to receive only in a certain limited angular range.